interface (Figure 1).  The domain name service is an application
independent network service for the resolution of domain names.  This
resolution is provided through the cooperation among a set of domain


                                   1
 
RFC 830                                                       October 1982



name servers (DNSs).  With each domain is associated a DNS.*  The reader
is referred to [2] for the specification of a domain name server.  As
noted in [1], a domain is an administrative but not necessarily a
topological entity.  It is represented in the networks by its associated
DNS.  The resolution of a domain name results in the address of its
associated DNS.


     Application                                   Application
       Process                                       Process
          |                                             |
   SINS   |                                             |
   -------|---------------------------------------------|-----  Application
   |     AIP                                           AIP   |   Interface
   |      |                                             |    |  . . . . . . .
   |     DNS  - - -  DNS  - - -  DNS  - -  . . .  - -  DNS   |  Domain Name
   -----------------------------------------------------------    Service

           Figure 1   Separation of Application Interface

     The application interface provides mechanisms for resolution beyond
that of destination domain and negotiation to ensure resource
availability and compatibility.  Such negotiation is sometimes referred
to as the "what-can-you-do-for-me" negotiation.  The application
interface isolates domain name service from application dependence.  It
thus allows sharing of domain name service among various user
applications.

     The application interface consists of a set of application
interface processes (AIPs) one for each endpoint domain.  For operation
efficiency, the AIP is assumed to be combined with its associated DNS
forming an endpoint DNS (Figure 2).


       Application                                   Application
         Process                                       Process
            |                                             |
     SINS   |                                             |
     -------|---------------------------------------------|-------
     |   Endpoint                                      Endpoint  |
     |     DNS  - - -  DNS  - - -  DNS  - -  . . .  - -  DNS     |
     |                                                           |
     -------------------------------------------------------------

    Figure 2  Distribution of Name Service Components Among Domains

--------------------
* For reasons such as reliability, more than one DNS per domain may be
required.  They may be cooperating DNSs or identical for redundancy.  In
either case, without loss of generality we may logically view the
association as one DNS per domain.


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RFC 830                                                       October 1982

2.2  Domain Resolution

     For name service, the source application process presents to its
local AIP the destination name, and the application service it requests.
For most applications, the application service the source application
process requests would be the service it offers.  The destination name
is assumed to be fully qualified of the form:

	   @.. ... .

The domains named in the concatenation are hierarchically related [1].
The left-to-right string of simple names in the concatenation proceeds
from the most specific domain to the most general.  The concatenation of
two domains,

		... ... ...

implies the one on the left, domain A, to be an immediate member (i.e.,
the first-generation descendent) of the one on the right, domain B.  The
right-most simple name designates a top-level domain, a first-generation
descendent of the naming universe.

     For domain resolution, the AIP consults the domain name service.  It
presents the co-located DNS with the fully qualified domain
specification:

		.. ... .

The DNSs participating in a resolution resolve the concatenation from
the right.  The source endpoint DNS resolves the right-most simple name
and acts as a hub polling the other DNSs.  It resolves the right-most
simple name into an address for the DNS of the specified top-level